Contraceptive methods and compositions

ABSTRACT

Introduction of a pharmaceutically acceptable non-toxic cation salt of a sterol sulfate into the uterine lumen or vaginal cavity prevents conception. Potassium or pyridinium β-sitosteryl sulfate is preferred.

This is a continuation-in-part of application Ser. No. 57,931, filedJuly 16, 1979, now abandoned which is a continuation of application Ser.No. 973,252, filed Dec. 26, 1978, now abandoned.

This invention relates to improved methods and compositions useful inhuman and veterinary medicine for the control of fertility.

Contraceptive methods involving the administration of chemicalsubstances are widely practiced among women who desire to limitpregnancies. Such methods control fertility through various biologicalmechanisms. Among the presently used chemical methods of fertilitycontrol, the most important are those which act by means of thefollowing: (a) suppression of ovulation through inhibition ofgonadotropin release; (b) alteration of the female reproductive tract toprevent migration of sperm to the site of fertilization or, iffertilization occurs, to block implantation of the zygote (nidation); or(c) spermicidal action.

The oral contraceptives are the most prominent chemical contraceptiveagents. These agents are of two types: (a) an estrogen combined with aprogestin, and (b) a progestin alone. The contraceptives of the combinedtype act primarily by suppressing ovulation by negative feedback toprevent gonadotropin (LH and FSH) release by the hypothalamus, butalterations in the reproductive tract may also contribute to theanti-fertility effect. Such alterations include changes in the cervicalmucus (which increase the difficulty of sperm migration) and in theendometrium (which decrease the likelihood of nidation). The action of aprogestin alone in a very low oral dose (the "mini-pill") appears toinvolve primarily alterations in the female reproductive tract, butovulation suppression may also occur. Although the oral contraceptivesare highly effective, their use is associated with unpleasant sideeffects (such as nausea, depression, weight-gain, and headache) and anincreased long-time risk of severe disease (such as thromboembolism,stroke, myocardial infarction, hepatic adenoma, gall bladder disease,and hypertension). Bleeding irregularities (such as break-throughbleeding, spotting, and amenorrhea) are also frequent. A progestin, whenadministered alone, causes an increased incidence of changes inmenstrual patterns, especially a marked increase in the amount andduration of menstrual bleeding.

Besides the oral route of administration a progestin alone may beadministered systemically by various sustained-release dosage formswhich include: (a) depo injection (IM) of an insoluble progestin (e.g.medroxy progesterone acetate), (b) a subdermal implant, or (c) anintravaginal insert. With these methods of administration, the progestinis absorbed into the body continuously at a very low daily dose, and thesystemic effects are similar to those produced by oral administration ofa progestin. However, as with the oral progestins, the sustained releasemethods may cause serious menstrual flow irregularities.

A recent method of contraception involves the sustained release ofprogesterone locally within the uterine lumen. In this method theprogesterone is incorporated into a chamber within a flexibleintrauterine device (IUD) formed from a polymer which is capable ofreleasing progesterone continuously into the uterine fluids at a slowrate over a prolonged period of time. The progesterone acts primarilylocally to produce progestational alterations in the cervical mucus andendometrium. However, the antifertility action may also be caused by thereaction of the endometrium to the device itself ("IUD effect") or bysystemic absorption of progesterone through the uterine membrane. Again,as with other progestin-only therapies, there is an increased incidenceof menstrual flow irregularities. Another disadvantage of this method,is the increased risk of ectopic pregnancy.

Another recent development is the flexible IUD bearing metallic copper.The contraceptive action of this device results from the combinedeffects of the copper (which very slowly dissolves in the uterinefluids), which acts on the blastocyst and on the cervical mucus orendometrium, and of the IUD itself, which causes a foreign body reactionin the endomentrium.

Other chemical methods of contraception include the post coitaladministration of estrogens (e.g. diethylstilbestrol orethynylestradiol) to prevent nidation or of prostaglandins which act asabortifacients. Both of these methods, at present, are limited toemergency situations. Still in the very early stages of development areimmunological methods (vaccination) and methods involving the directcontrol of LHRH secretion from the pituitary by LHRH agonists orantagonists.

Another group of chemical contraceptive agents are the localspermatocides, such as nonoxynol or octoxynol, which are placed into thevagina immediately prior to coitus in the form of creams, foams,jellies, or suppositories. The spermicidal action takes place either inthe vagina or elsewhere in the reproductive tract. For the latter tooccur, the spermicidal agent is either adsorbed on sperm membranes or istransported into the uterus under the influence of uterine contractions.The spermicidal methods are less reliable in preventing pregnancy andare inconvenient to use. The intrauterine device (IUD) is the mostcommon alternative to the oral contraceptives. The anti-fertility effectof the IUD is not caused by chemical activity. Instead the materialforming the IUD induces a foreign body reaction (irritation) in thecontiguous endomentrium which appears to interfere in some way withnidation. The use of the IUD is complicated, however, by seriousproblems including the possibility of intrauterine perforation, pelvicinflammation, discomfort, or aggravated menstrual periods.

From the foregoing, it is evident that the presently available methodsof contraception are inadequate for various reasons because they: (a)may produce unpleasant side effects or increase the risk of seriousdisease, (b) may be unreliable, or (c) may be inconvenient and intrudeon sexual enjoyment. Although many women practice contraception in spiteof these inadequacies, a need exists in medicine for improved methodswhich combine effectiveness with increased safety and convenience. Suchimprovements are afforded by the present invention.

It has now been surprisingly found that a class of sterol sulfate salts(to be more fully described below) will effectively preventfertilization when introduced in very small amounts in the femalereproductive tract prior to coitus. The sterol sulfate salts do notproduce hormonal effects either locally or systemically, and, hence,they offer significant advantages over the oral contraceptive steroidsand the sustained release progestin compositions heretofore used. Theantifertility effect of the sterol sulfate salts has been demonstratedin female rabbits using standard pharmacological test procedures wherebythe test compound is introduced locally within the reproductive tract ofthe animal, the animal is then bred to a fertile buck, and the genitalsystem of the animal is then examined to determine the number ofembryos.

The sterol sulfate salts can be delivered satisfactorily within thefemale reproductive tract by slow release from silicone rubbercompositions. Silicone rubber is known to be a useful vehicle for thesustained delivery of certain medicaments. Administration of a sterolsulfate salt in the female reproductive tract by means of a sustainedrelease silicone rubber composition will provide a more convenient andacceptable method of contraception than has heretofore been employed inthe prior art.

The invention sought to be patented in its method of use aspectsconstitutes:

1. A method of contraception in a female mammal which comprisescontinuously introducing within the uterine lumen of said female, over aprolonged period of time at a controlled rate, an effective amount of apharmaceutically acceptable, non-toxic cation salt of a sterol sulfatederived from cholesterol, campesterol, β-sitosterol, lanosterol,ergosterol, 7-dehydrocholesterol, or 3β-hydroxycholenic acid.

2. A method of contraception in a female mammal which comprisescontinuously introducing within the vaginal cavity of said female, overa prolonged period of time at a controlled rate, an effective amount ofa pharmaceutically acceptable, non-toxic cation salt of a sterol sulfatederived from cholesterol, campesterol, β-sitosterol, lanosterol,ergosterol, 7-dehydrocholesterol, or 3β-hydroxycholenic acid, wherebysaid sterol sulfate salt is transported into the uterine fluids withsperm during or after coitus; or

3. A method of contraception in a female mammal which comprisesintroducing into the vaginal cavity immediately before coitus aneffective amount of a pharmaceutically acceptable, non-toxic cation saltof a sterol sulfate derived from cholesterol, campesterol, β-sitosterol,lanosterol, ergosterol, 7-dehydrocholesterol, or 3β-hydroxycholenicacid, whereby said sterol sulfate salt is transported into the uterinefluids with sperm during or after coitus.

In its composition aspects, the present invention contemplates:

1. A contraceptive composition suitable for insertion and comfortableretention in the uterine lumen which comprises: (a) about 1 to about 40percent by weight of a pharmaceutically acceptable, non-toxic cationsalt of a sterol sulfate derived from cholesterol, campesterol,β-sitosterol, lanosterol, ergosterol, 7-dehydrocholesterol, or3β-hydroxycholenic acid and (b) about 60 to about 99 percent by weightof a biocompatible, bioinsoluble, flexible silicone rubber carriermatrix, said matrix being capable of continuously releasing said sterolsulfate salt into the uterine fluids at a controlled rate over aprolonged period of time; or

2. A contraceptive composition suitable for insertion and comfortableretention in the vaginal cavity which comprises: (a) about 1 to about 40percent by weight of a pharmaceutically acceptable, non-toxic cationsalt of a sterol sulfate derived from cholesterol, campesterol,β-sitosterol, lanosterol, ergosterol, 7-dehydrocholesterol, or3β-hydroxycholenic acid and (b) about 60 to about 99 percent by weightof a biocompatible, bioinsoluble, flexible silicone rubber carriermatrix said matrix being capable of continuously releasing said sterolsulfate salt into the vaginal fluids at a controlled rate over aprolonged period of time; or

3. A contraceptive foam, jelly, cream, suppository, or spongecomposition suitable for comfortable insertion into the vaginal cavityimmediately prior to coitus which comprises: (a) an effective amount ofa pharmaceutically acceptable, non-toxic cation salt of a sterol sulfatederived from cholesterol, campesterol, β-sitosterol, lanosterol,ergosterol, 7-dehydrocholesterol, or 3β-hydroxycholenic acid, and (b) apharmaceutically acceptable, non-toxic vaginal excipient.

The sterol sulfate salts used in the contraceptive methods andcompositions herein described have the formula:

    R--OSO.sub.3 M                                             I

wherein R represents the sterol nucleus of cholesterol, campesterol,β-sitosterol, lanosterol, ergosterol, 7-dehydrocholesterol, and3β-hydroxycholenic acid; and M is a pharmaceutically acceptablenon-toxic cation (e.g. sodium, potassium, lithum, calcium, magnesium,copper, aluminum, zinc, pyridinium, substituted pyridinium, ammonium, orsubstituted ammonium). It will be appreciated by those skilled in theart that when the cation (M) has a valency greater than one, more thanone sterol sulfate moiety will be associated with the cation. Thesterols named above are known in the art. The pyridinium sulfate saltsof the sterols are prepared by reacting the desired sterol with pyridinesulfate trioxide according to the method of A. Sobel et al., J. Am.Chem. Soc. 63, 1259 (1941). Each sterol pyridinium salt wasrecrystallized to a constant melting point which agreed with literaturevalue and showed only one spot in various TLC systems. Other salts canbe prepared by methods well known in the art of chemistry. The sterolsulfates can be assayed by a method comprising acid hydrolysis to formthe corresponding sterol, extracting the sterol, and determining itsamount by gas chromatography.

The sterol sulfate salts represented by Formula I control fertility byinhibiting an enzyme which is required during fertilization to allowsperm to penetrate the outer investments of the ovum. An ovum containsthree outer investments-the cumulus oophorus, the corona radiata, andthe zona pellucida--which are barriers to fertilization. In the male andwhen first deposited in the female, sperm is incapable of fertilizing anovum since it lacks the capacity to penetrate the outer investments.Before fertilization can occur, specific hydrolytic enzymes emanatingfrom the sperm must digest each investment so as to form a passage forsperm penetration. The process by which sperm achieve the ability topenetrate the ovum is known as "capacitation." Capacitation involves thelabilization of sperm membranes and the release, activation, or exposureof the ovum penetrating enzymes as needed to attack each investment.There is evidence that the activation of the ovum penetrating enzymesmay involve the removal of specific inhibitors of the enzymes. The exactbiochemical transformations occurring during capacitation are not fullyunderstood, but the enzymes must exert their action either while boundto the sperm membranes or upon release from sperm after the sperm andthe ovum make contact in the fallopian tube. For a review of thebiochemistry of capacation and of the inhibition of the ovum penetratingenzymes see McRorie et al., Am. Rev. Biochem., 43, 777 (1974) and E.S.Hafez, Ed., "Human Semen and Fertility Regulation in Men, " C. V. MosbyCo., St. Louis, Mo., 1976, pages 201 to 242 and 563 to 582.

It has been found that the sterol sulfate salts of Formula I inhibit invitro the action of acrosin, the sperm acrosomal enzyme which is knownto be responsible in vivo for the penetration of the zona pellucida bycausing degradation of the glycoproteins of the zona pellucida.Inhibition of acrosin in vivo will lead to interruption of the ovumpenetration process thereby effectively preventing fertilization andpregnancy. The β-sitosteryl sulfate salts are the most effectiveinhibitors of acrosin and are preferred.

The ability of the sterol sulfates to prevent digestion of the zonapellucida is demonstrated in in vitro tests wherein an isolated ovumfrom a rabbit is observed under a microscope while being incubated incalcium-free Ringer's solution in the presence of acrosin with andwithout the sterol sulfate being present in the medium. In the absenceof cholesteryl pyridinium sulfate, or β-sitosteryl pyridinium sulfate,complete removal of the zona pellucida is observed. With the compoundpresent, the zona pellucida remains substantially intact.

In order to prevent pregnancy, an effective, amount of the sterolsulfate salt must be present at the site of fertilization in thefallopian tube when sperm and the ovum make contact prior to penetrationof the ovum. The sterol sulfate salt can be administered by introductionlocally either within the uterine lumen or vaginal cavity. By both modesof administration, the sterol sulfate salt is carried to the site offertilization either by adsorbtion onto sperm membranes or by transportthrough the fluids of the reproductive tract. In uterine fluids, thesterol sulfate salt reaches the fallopian tube by means of diffusion oractive transport. In vaginal fluids, the compound passes to the uterinefluids either adsorbed on sperm membranes or by active transport underthe influence of uterine contractions. The preferred method ofadministration from the standpoint of convenience to the female user isto introduce the sterol sulfate salt continously within the uterus orvagina during the fertile period of the female (i.e. the period three tofour days after ovulation when an ovum is present in the fallopiantube). By this method an effective amount of the active compound ispresent within the reproductive tract each day to prevent fertilizationif coitus should occur during the fertile period. Such a method would beindependent of the sex act and would avoid the inconvenience of repeatedindependent dosages.

The continuous administration of the active compound can be accomplishedeffectively by incorporating it into an organopolysiloxane (siliconerubber) composition and placing said composition into the uterine lumenor vaginal cavity. The compound is slowly introduced into the uterine orvaginal fluids by release from the silicone rubber at a controlled rate,an effective amount of the compound being present continuously in suchfluids. The silicone rubber acts as an insoluble carrier matrix forsupporting the active compound while it is being introduced into theuterine or vaginal fluids. Silicone rubber is bioinsoluble andbiocompatible (i.e. it is non-toxic, insoluble, and physiologicallyinert when in contact with body tissues and fluids) and is flexibleenough to avoid uterine perforation and to prevent or mimimize an IUDeffect on the contiguous endometrium. The silicone rubber carrier can beformed in any shape or size suitable for insertion and comfortableretention in the uterine lumen or vaginal cavity. For example, forintrauterine use it can be in the form of a Lippes loop, butterfly,coil, Birnberg bow, or T configuration, or modifications thereof, whichconfigurations are well known in the art to be useful for retention inthe uterus. [See, for example, U.S. Pat. Nos. 3,234,938; 3,533,406;3,935,860; 3,077,879; 3,250,271; and 3,319,625.] For intravaginal use,it can be formed as a flexible ring, similar in configuration to that ofthe retaining ring of a diaphragm, which is known in the art to beuseful for retention in the vagina. [See, U.S. Pat. Nos. 3,545,439 and3,920,805.]

Organopolysioxanes are described in U.S. Pat. No. 3,279,996 (Long etal), the disclosure of which is incorporated herein by reference. Thispatent describes implants for releasing a drug in the tissues of livingorganisms comprising the drug enclosed in a capsule formed of siliconerubber or the drug dispersed in a prosthesis made from silicone rubber.A number of biocompatible insoluble silicone rubbers are described inthe Long et al. patent. A preferred silicone rubber isdimethylpolysiloxane which is curable at room temperature or above withan appropriate curing agent. Suitable dimethylpolysiloxane rubbers aresold commercially as liquid elastomers which are mixed with a curingagent to obtain the solid rubber. Among such commercially availablerubbers are those sold by Dow-Corning Corporation identified as Silastic382 and MDX-4-4210. Such rubbers consist of two components, a firstcomponent comprising liquid uncured rubber, and a second componentcomprising a curing agent. The two components are mixed and the mixtureis allowed to cure. Heating can be employed to enhance curing, ifdesired. Another suitable type of dimethylpolysiloxane rubber is a highconsistency medical grade elastomer such as that sold by Dow-Corningcorporation under the designation MDF-0198. For preparing carriercompositions suitable for intrauterine or intravaginal use, the activecompound, preferably in a very fine particle size, in the amount desiredis throughly mixed mechanically with the uncured dimethylpolysiloxanerubber. The curing agent is then added, and the mixture is placed, e.g.by injection, in a mold having a cavity of the desired size and shape.The elastomer is allowed to cure at an appropriate temperature and time.Upon completion of the curing, the molded composition is removed at roomtemperature. Using the above described procedure there is obtained adimethylpolysiloxane in which the active compound is uniformlydispersed. When in contact with body fluids in which the compound issoluble (i.e. the uterine or vaginal fluids), the compound is releasedinto the fluids.

It will be recognized by those skilled in the art that the siliconerubber compositions useful for the purposes of this invention can bemade by other methods which are conventional in the art. One method isto form a silicone rubber composition containing the dispersed activecompound, using the molding technique described above, and then to coatthe composition with a very thin layer of silicone rubber. For example,a formed silicone rubber rod containing dispersed active compound can becoated with silicone rubber using conventional coating, bonding, orlaminating techniques, such as by immersing the rod in a solution ofuncured silicone rubber in a volatile solvent, removing the rod,evaporating the solvent, and curing the coating of silicone rubberformed thereby by heating. Alternatively, the rod containing thedispersed active compound can be fitted tightly inside a very thinhollow silicone rubber tube and the ends can be sealed. If desired, thesilicone rubber composition containing the active compound can be coatedwith, or enclosed tightly within, a microporous material through whichthe compound can pass by microporous flow, when the finished compositionis bathed in vaginal or uterine fluids. The microporous material can bea microporous silicone rubber or other microporous polymer, the choiceand use of which will be apparent to those skilled in the art.

Another method of making the compositions is by coating silicone rubbercontaining the dispersed active compound on an inert, biocompatible,insoluble, flexible core material. Preferably, the inert core is formedfrom silicone rubber, but other suitable conventional materials can beused.

It will also be understood that an effective amount of the activecontraceptive compound can be releasably affixed to the outer surface ofthe silicone rubber compositions, so that, when the composition isinserted into the uterus or vagina, there is an immediate release of thecompound into the body fluids. The compound can be deposited or coatedon the medicated silicone rubber composition using conventional methods.

It will be apparent to those skilled in the art that, if desired, aneffective amount of an X-ray contrast agent (e.g. barium sulfate) can beincluded in the compositions of the invention in order to render thecompositions opaque to X-rays. It will also be apparent that, ifdesired, a non-toxic pharmaceutically acceptable filler can be added tothe silicone rubber. The use of such fillers are well known in the art.

In general, the concentration of the active compound in the siliconerubber carrier composition may vary from about 1 to about 40 percent byweight. A preferred range is from about 5 to about 20 percent. Aconcentration of about 10 percent has been found to be most preferred.

The rate of release of the active compound can be assessed by an invitro test wherein the medicated carrier is placed in fresh water orfresh calcium-free Ringer's solution at 37° for successive periods oftime (e.g. 24 hours), and the amount of active ingredient released aftereach period is assayed from a determination of the acrosin inhibitingactivity of the solution. For intrauterine use, a release rateequivalent to from about 1 to about 200 μg. of the active compound perday is desired. A rate from about 50 to about 150 μg. per day ispreferred. For intravaginal use, a release rate of about 1 to about 5mg. per day is desired.

It is desirable that the rate of delivery be substantially constant overthe period in which the carrier composition is present in the uterinelumen or vaginal cavity. The duration of drug delivery should cover atleast the fertile period of the female. Of course, for maximumconvenience to the female, the delivery should extend over a prolongedperiod of time, preferably with intrauterine use one year or more, sincethis will avoid the inconvenience of repeated removal and reinsertion ofthe medicated carrier. For intravaginal use, the carrier composition ispreferably removed at the start of the menstrual period and isreinserted after bleeding stops.

For administration to females, who for personal reasons do not wish touse a sustained release medicated intrauterine or intravaginalcomposition, an alternative method of administration of the activecompound is by means of a pharmaceutically acceptable jelly, foam,cream, or suppository, which is inserted into the vagina immediatelyprior to coitus in a manner similar to that employed for administeringspermicidal compositions. The jelly, foam, cream, or suppository acts asa vehicle for carrying an effective amount of the active ingredient intothe vaginal fluids from where it is carried into the uterus byadsorption on sperm membranes or by active transport. The activeingredient can be compounded into vaginal jellies, foams, creams, orsuppositories according to procedures which are conventional in the art,by employing the usual excipients (buffer, emulsifier, preservatives,and the like), the choice and amount of which will be apparent to thoseskilled in the art.

For reasons of convenience, esthetics, or more precise control ofdosage, a vaginal suppository is preferred. The suppository compositionmust be chemically and physically stable under conditions of storage andhandling, and also must be capable of melting and/or dissolving wheninserted in the vagina to effect satisfactory release of the activecompound into the vaginal fluids. A preferred suppository compositioncomprises an effective amount of the active compound in a suitablepolyethylene glycol vehicle. Various polyethylene glycols, either aloneor in combination, are known in the art to be useful for making vaginalsuppository compositions, and the choice of a particular vehicle will beapparent to those skilled in the art.

For intravaginal use, an effective amount of the active compound can beabsorbed into a biocompatible, bioinsoluble, non-toxic sponge-like softpolymer, which when inserted and retained in the vagina will release thecompound by desorption into the vaginal fluids. The sponge can beallowed to remain in the vagina during coitus or it can be removed priorto coitus. Suitable polymers for this use are well known in the art, forexample, a hydrophilic polymer, such as polymeric 2-hydroxyethylmethacrylate which, if desired, may contain a cross-linking agent (e.g.dimethacrylate).

The following examples illustrate the methods and compositions of thepresent invention.

EXAMPLE 1 Acrosin Inhibition In Vitro

The inhibition of acrosin is assessed in vitro using benzoyl argininep-nitroanilide (BAPNA) as the enzyme substrate according to thefollowing procedure: Acrosin (200 μl, purified from boar sperm) and asolution (200 μl.) of the test compound (10 mg./ml.) in 0.05 Mtriethanolamine buffer, pH 7.8, are incubated at room temperature for 5minutes. A control using the buffer solution without the test compoundadded is also run. A 200 μl.-sample of the incubation mixture is thenwithdrawn and is added to a cuvette containing BAPNA (1 ml.) andtriethanolamine buffer (2 ml.). The mixture is stirred and placed in aGilford recording spectrophotometer. The increase in optical density at383 nm is measured. One unit of acrosin activity is defined as theamount of acrosin which will cause an increase in optical density at 383nm of 0.001/minute. One unit of inhibitory activity is defined as theamount of inhibitor which will cause a reduction in the increase inoptical density at 383 nm. of 0.001 /minute.

The results of the testing of sterol sulfates of Formula I, as theirpyridinium salts, for acrosin inhibition using the above describedprocedure are shown below in Table I.

                  TABLE I                                                         ______________________________________                                        In vitro acrosin inhibition of pyridinium sterol sulfates                                          Inhibition                                               Sterol               (Units/mg.)                                              ______________________________________                                        cholesterol          50,000                                                   campesterol          20,000                                                   β-sitosterol    60,000                                                   lanosterol           46,000                                                   ergosterol           11,000                                                   7-dehydro-                                                                    cholesterol          43,000                                                   3β-hydroxy-                                                              cholenic acid        14,000                                                   ______________________________________                                    

EXAMPLE 2 Preparation of Medicated Dimethylpolysiloxane RubberComposition

In a suitable container there are mixed 2430 mg. of dimethylpolysiloxaneelastomer (Dow-Corning MDX-4-4210), 270 mg. of curing agent (Dow-CorningMDX-4-4210) and 300 mg. of potassium β-sitosteryl sulfate. After mixing,the mixture is placed in a 3 ml. syringe (no needle) and injected into astainless steel mold block, containing two cylindrical mold cavities.The block is placed in a vacuum oven at 90° C. (slight vacuum) for about1 hour. Upon cooling (after about 10 to 15 minutes) the moldedcompositions are removed to give 2 rods 3 mm. in diameter and 63 mm. inlength. The content of potassium β-sitosteryl sulfate in eachcomposition is 10% (W/W). Following the same procedure but using 2565mg. of elastomer, 285 mg. of curing agent, and 150 mg. of potassiumβ-sitosteryl sulfate, there is obtained dimethylpolysiloxanecompositions containing 5% of active ingredient.

EXAMPLE 3 Determination of drug release rate from dimethylpolysiloxanerubber compositions

An appropriate sample of a dimethylpolysiloxane rubber composition inwhich is incorporated the test compound is placed in a suitable amountof calcium-free Ringers solution, and the sample and solution areincubated together at 37° C. for a period of time (e.g. 24 hours). Thesolution is removed and assayed for acrosin inhibition (expressed asunits per milligram) using the technique described in Example 1. Theequivalent amount of test compound in the removed solution is calculatedfrom standard inhibition curves in which acrosin inhibition is plottedagainst concentration of the test compound. The calculated result areexpressed as micrograms of test compound released per day.

The above test may be repeated over an extended period of time, forexample, for 1 day to 360 days, or more, by adding fresh calcium-freeRinger's solution after each removal of the solution for assay.

Samples of a dimethylpolysiloxane rubber composition containing 10% W/Wof potassium β-sitosteryl sulfate were tested as above described for 16days. The sample weight was 40 mg. and the amount of added solution was1 ml. After the 16th day, the release rate from the samples averaged 1-2micrograms/day.

EXAMPLE 4 Antifertility effects, in vivo A. By intrauterineadministration

Dutch Belted virgin rabbits, each weighing 3-4 pounds, are randomlyselected and anesthetized with sodium pentobarbital (50 μg/ml.)administered by IV drip. The uterus of each animal is exposed and a40-mg. sample in the shape of a rod (3 mm. in diameter) ofdimethylpolysiloxane rubber (as prepared in Example 3 ) containing 10%W/W of potassium β-sitosteryl sulfate is sutured into the right uterinehorn at a random location in between the cervix and the utero-tubaljunction. The left horn is left untreated to serve as control. Therubber rod is placed into the uterine horn by passing a curved needlethrough it and through the uterine wall pulling the rod into the uterinelumen. The entry is closed by suturing. Animals (blank) are similarlytreated using unmedicated dumethylpolysiloxane rubber to serve as asecond group of controls. The animals are given 300,000 units ofDuracillin® per day (in four doses) and are allowed to recover for 14days. Each animal is bred to a male of proven fertility and isimmediately given a dose (IV) of approximately 100 units of humanchorionic gonadotropin (HCG) to facilitate ovulation. Fourteen daysafter breeding, the animals are sacrificed by cervical dislocation andthe uterine horns are examined for inplanted embryos. The number ofembryos per uterine horn are recorded.

A comparison of implanted embryos in untreated horns, in blank horns,and in treated horns is set forth below in Table II.

                  TABLE II                                                        ______________________________________                                        Inhibition of fertilization by potassium β-sitosteryl                    sulfate slowly released in the uterus                                                             Total No.                                                  Treatment                                                                              Uterine hornsNumber of                                                                   embryos of                                                                              ##STR1##                                       ______________________________________                                        Untreated 32         77        2.4 ± 1.5                                   Blank     10         22        2.2 ± 0.99                                  Potassium                                                                     β-sitosteryl                                                             sulfate   10          3         .3 ± .5                                    ______________________________________                                         *Release rate from dimethylpolysiloxane, 1-2 μg./day, in vitro (Calc.      on basis of acrosin inhibition).                                         

It should be noted that in the blank animals the number of embryos perhorn is smaller. This is because the sutured material decreases theavailable area for implant of the fertilized ovum. However thedifference between the number of embryos in the untreated and in theblank animals is not statistically significant.

B. By intravaginal administration

Equal volumes of Ky-jelly® and either Ca⁺⁺ free Ringers solution or a 10mg./ml. solution of the compound to be tested in Ca⁺⁺ free Ringerssolution are well mixed. One milliliter of this is placed into thevagina of a virgin Dutch belted female rabbit using a syringe. Thefemale is then immediately bred to a fertile buck. The female isinjected I.V. with 100μ of human chorionic gonadotrophin to assure agood ovulation rate.

After approximately 14 days the females are sacrificed by cervicaldislocation and the genital system examined for the number of embryos.

When tested as above described β-sitosteryl sulfate, as the potassiumsalt gave the results shown below in Table III.

                  TABLE III                                                       ______________________________________                                        Inhibition of fertilization by potassium β-sitosteryl                    sulfate in female rabbits by intravaginal administration                      Treat-                         Avg. No. of                                    ment   No. of animals                                                                            No. of embryos                                                                            Embryos per animal                             ______________________________________                                        blank  3           15          5.0                                            treated                                                                              6           11          3.7                                            ______________________________________                                    

EXAMPLE 5 Removal of Zona Pellucida from ova, in vitro

Female rabbits are given 100 units of pregnant mares serum (PMS), IM,and 134 units of HCG, IV. After 13 hours the animals are sacrificed andthe ovaries are excised. The ovaries are submerged in calcium-freeRinger's solution. Ova are removed and and placed in 1 ml. ofcalcium-free Ringer's solution. The solutions are all shaken vigorouslyfor 5 to 10 minutes, which rids the ova of the cumulus oophorus and thecorona radiata. Acrosin (isolated from boar sperm) (100 μl., of asolution containing 2000 U/ml. in 0.1 M sodium acetate and 0.02 Mcalcium chloride) is added to each of 10 ova. To each of 10 other ova inthe same medium is added 10 μl. of solution pyridinium β-sitosterylsulfate (10 mg./ml.) in calcium-free Ringer's solution. To 10 other ovais added 10 ml. of calcium-free Ringer's solution as a control. Thesolutions are all incubated at 37° C. The zona pellucida is observed at15 minute intervals with an American Optical stereomicroscope. In theabsence of pyridinium β-sitosterol sulfate, the zona pellucida iscompletely removed. With the compound sulfate present, the zonapellucida remains substantially intact.

What is claimed is:
 1. A contraceptive composition suitable forinsertion and comfortable retention in the uterine lumen whichcomprises: (a) about 1 to about 40 percent by weight of apharmaceutically acceptable, non-toxic cation salt of a sterol sulfatederived from cholesterol, campesterol, β-sitosterol, lanosterol,ergosterol, 7-dehydrocholesterol, or 3β-hydroxycholenic acid and (b)about 60 to about 99 percent by weight of a biocompatible, bioinsoluble,flexible silicone rubber carrier matrix, said matrix being capable ofcontinuously releasing said sterol sulfate salt into the uterine fluidsat a controlled rate over a prolonged period of time.
 2. A compositionas defined in claim 1 wherein the silicone rubber isdimethylpolysiloxane.
 3. A composition as defined in claim 1 or 2,wherein the sterol sulfate is β-sitosterol sulfate.
 4. A composition asdefined in claim 3 wherein the cation is potassium or pyridinium.